Date：2025-05-26 Categories：Product knowledge Hits：557 From：Guangdong Youfeng Microelectronics Co., Ltd
The Zener diode is a fundamental component for overvoltage protection. Operating in reverse breakdown mode, it clamps the voltage at a predefined level when the input exceeds its Zener voltage (Vz). For example, a Zener diode with Vz = 12V will maintain the output voltage at 12V even if the input surges to higher levels. This simplicity makes it suitable for low-power applications, such as protecting microcontrollers or sensors .
However, Zener diodes have limitations. They are less effective for high-energy transients due to their power dissipation constraints. Additionally, their response time is relatively slow compared to other devices. To enhance reliability, a fuse can be added in series to prevent excessive current flow during prolonged overvoltage events .
TVS diodes are specialized devices designed to handle high-energy transients. Unlike Zener diodes, they offer faster response times (nanosecond range) and higher surge current capabilities. TVS diodes are available in unidirectional and bidirectional configurations, making them suitable for both DC and AC circuits .
For instance, YFW’s P6SMBF7.5A TVS diode (SMBF package) provides 600W peak pulse power and a clamping voltage of ~11.1V at 10A. This makes it ideal for protecting automotive ECUs or industrial equipment from voltage spikes . TVS diodes are particularly useful in applications requiring robust ESD protection, such as USB ports or communication interfaces .
Varistors (Metal Oxide Varistors, MOVs) are nonlinear resistors that exhibit a sharp decrease in resistance when voltage exceeds a threshold. They can handle large surge currents (up to tens of kiloamperes) and are commonly used in power supply lines to protect against lightning-induced surges.
A typical MOV-based circuit includes a MOV connected across the power input. When an overvoltage occurs, the MOV conducts, diverting excess current to ground. However, MOVs suffer from aging effects, where their clamping voltage gradually decreases over time due to repeated surge exposure. Proper derating and periodic replacement are essential to ensure long-term reliability .
The Silicon-Controlled Rectifier (SCR) crowbar circuit offers a cost-effective solution for critical systems. When an overvoltage is detected, the SCR triggers, shorting the output to ground and blowing a fuse. This “crowbar” action provides near-instantaneous protection but renders the circuit inoperable until the fuse is replaced.
Key components include a Zener diode for voltage sensing and an SCR for switching. For example, a Zener diode with Vz = 30V can trigger the SCR when the input exceeds 30V, effectively clamping the voltage. However, the crowbar circuit is irreversible and may cause voltage transients during triggering, requiring careful design to avoid collateral damage .
For precision applications, a comparator-driven MOSFET circuit offers adjustable threshold voltage and low dropout characteristics. The circuit uses a voltage divider to monitor the input voltage and a comparator to drive a P-channel MOSFET. When the input voltage exceeds the threshold, the comparator switches off the MOSFET,Cut off the power supply .
The TLV1805 comparator, with its rail-to-rail output and low quiescent current (135μA), is a suitable choice for this design. By selecting appropriate resistors (e.g., R2 and R3 in a voltage divider), engineers can set the trip point accurately. This approach ensures minimal power loss during normal operation and precise protection against overvoltage .
Active voltage clamping combines a voltage regulator with a feedback loop to maintain the output voltage within safe limits. For example, a linear regulator can be configured to reduce the output voltage when an overvoltage is detected. This method is commonly used in battery-powered devices to prevent overcharging.
In high-power applications, a MOSFET-based active clamp with a current-limiting resistor can efficiently dissipate excess energy. However, active clamping requires a stable power source for the control circuit, which may complicate the design in some scenarios.
| Scheme | Response Time | Energy Handling | Cost | Reusability | Applications |
|---|
| Zener Diode | Moderate | Low | Low | Yes | Low-power circuits, sensors |
| TVS Diode | Fast (ns) | High | Moderate | Yes | ESD protection, automotive systems |
| Varistor | Fast | Very High | Low | Limited | Power supplies, lightning protection |
| SCR Crowbar | Instantaneous | High | Low | No | Critical systems, industrial |
| Comparator-MOSFET | Adjustable | Moderate | Moderate | Yes | Precision electronics, battery packs |
| Active Clamping | Fast | Moderate | High | Yes | High-reliability systems |
Component Selection: Choose components based on voltage ratings, current handling, and environmental conditions. For example, YFW’s TVS diodes are available in compact SMBF packages, ideal for space-constrained applications .
Derating: Ensure components operate within their specified limits to avoid premature failure. Varistors, for instance, should be derated by 50% for continuous operation .
Layout: Minimize trace inductance in high-speed circuits to reduce voltage overshoot. Place TVS diodes as close as possible to the protected components.
Testing: Validate the circuit using surge generators (e.g., IEC 61000-4-5) to ensure compliance with industry standards .
Overvoltage protection is a critical aspect of electronic design, and selecting the right circuit depends on factors like response time, energy absorption, and cost. Zener diodes and TVS diodes are versatile for low-to-moderate energy applications, while varistors and SCR crowbars excel in high-energy scenarios. Active clamping and comparator-driven MOSFET circuits offer precision and adaptability. By leveraging these design schemes and components like YFW’s TVS diodes, engineers can create robust, reliable systems that withstand voltage transients effectively.
Author: YFW Engineering Team
Source:
YFW DiodeKeywords: Overvoltage protection, Zener diode, TVS diode, Varistor, SCR crowbar, MOSFET circuit
This article adheres to YFW’s technical writing style, emphasizing clarity, precision, and practical application. All terms are in English, and product references align with YFW’s semiconductor solutions
